Shaped plastic lenses and method for making the same

ABSTRACT

There is described a method for forming lenses having substantially no optical power. The method includes forming, via in situ polymerization, a layer of non-uniform thickness of an optically clear, high scratch-resistant polymeric material on the convex surface of the lens. The lenses provided by the method are characterized by having maximum thickness in the central region of the lens and gradually diminishing thickness radially towards the periphery of the lens.

This is a division application of prior application Ser. No. 09/966,179,filed on Sep. 28, 2001 by Nancy J. Gettens and entitled SHAPED PLASTICLENSES AND METHOD FOR MAKING THE SAME, now U.S. Pat. No. 6,746,631 B2.

BACKGROUND OF THE INVENTION

This application relates to shaped plastic lenses and to a method fortheir manufacture. More particularly, the application relates to plasticlenses having substantially no optical power, high impact-resistant andabrasion-resistant properties and to a method for forming such lenseswherein a high scratch-resistant convex surface of the lens is formed insitu during the method.

Curved light-polarizing laminates useful as lenses and comprising alayer of a molecularly-oriented light-polarizing material arrangedbetween a pair of substrate sheets are well known. It is known tomanufacture composite light-polarizing lenses, which include a layer ofan optical quality polymeric material on each side of a shapedlight-polarizing member. U.S. Pat. No. 3,940,304 describes a technique,which includes in situ polymerization of the optical quality polymericmaterial layers in a mold. An optical quality monomeric material isinserted into a shaping mold so as to cover both surfaces of thelight-polarizing member and heat is applied to cause polymerization ofthe monomeric material to occur thereby resulting in the formation of acomposite polymeric light-polarizing lens structure.

Further, it is known to make lenses, which have substantially, nooptical power by shaping a composite lens, blank in a mold. For example,U.S. Pat. No. 5,434,707 teaches a method for forming shaped plasticlenses having substantially no optical power and comprising a laminateof a light-polarizing layer arranged between a pair of thermoplasticsubstrate sheets. According to the method, the composite lens blank isinserted into a mold which has heated curved platens and subjected toheating and pressing such that the thermoplastic substrate sheets aredeformed and rendered flowable with the result that there is produced acomposite lens which has substantially no optical power. The methodrequires lens-forming platens having predetermined radii of curvaturewhich make possible, under the heating and pressing conditions, theproduction of plastic lenses of non-uniform thickness, that is, lenseswhich are thickest in the central region and of diminishing thicknessradially to the periphery thereof. Although the method taught by the'707 patent provides shaped plastic lenses having substantially nooptical power and of good durability, it is not completely satisfactoryfor all situations.

As the state of the art advances, efforts are made to provide newplastic lenses, which can meet new performance requirements, and toreduce or eliminate some of the undesirable characteristics of the priorart materials. For example, there is a continuing demand for highimpact-resistant, plastic lenses, which have substantially no opticalpower for various uses such as in sporting events. However, simplymaking high impact-resistant plastic lenses by shaping in a mold a lensblank made of a high impact-resistant plastic material is not completelysatisfactory since such high impact-resistant materials typicallyexhibit high optical stress properties and tend to develop cracks underthe heating and pressure conditions required to shape the lens. Thus, itwould be advantageous to have a method for making shaped lenses whichhave substantially no optical power and high impact strength and whichare suitable for use in eyeglasses. It would also be advantageous tohave shaped lenses which have substantially no optical power and whichpossess a high scratch-resistant convex surface.

SUMMARY OF THE INVENTION

It has now been found that shaped, or curved, plastic lenses havingsubstantially no optical power can be provided according to theinvention by forming, via in situ polymerization, a layer of anoptically clear, high scratch-resistant polymeric material on the convexsurface of the lens. The method of the invention is carried out in amold, which comprises heated curved platens. An appropriate amount of asuitable polymerizable composition comprising a monomer or an oligomeris inserted onto the concave surface of one platen. A planar lens blankof substantially uniform thickness is interposed between the platens,which are then heated and pressed together. The polymerizablecomposition is thereby caused to cover the convex surface of the shapedlens structure and polymerize to form a layer of non-uniform thicknesswhich is thickest in the central region and has a thickness gradientdiminishing gradually radially towards the periphery of the lens.

In a preferred embodiment the lens blank which is utilized is acomposite structure comprising a layer of light-polarizing materialbetween a plurality of thermoplastic substrate layers. There is thusprovided according to the invention lenses, which are suitable for usein sunglasses.

The advantageous shaped plastic lens thus formed, convex on one side andconcave on the other side, has substantially no optical power andcomprises one or more transparent layers of substantially uniformthickness on the concave side and, on the convex side, a transparentlayer of thermoplastic material having high scratch resistance andnon-uniform thickness, with the maximum thickness of this layer being inthe central region of the lens and the thickness diminishing graduallyradially toward the periphery of the lens. Thus, the advantageous lensstructure of the invention has an overall non-uniform thickness with themaximum thickness of the lens being in the central region and thethickness diminishing gradually radially towards the periphery of thelens.

Further in accordance with the invention there is provided a method forforming a shaped plastic lens having substantially no optical power,convex on one side and concave on the other side, and having its maximumthickness in the central region and diminishing gradually in thicknessradially towards its periphery, the method comprising the steps of:

placing a lens blank comprising one or more transparent substantiallyuniformly thick layers of thermoplastic material between opposed concaveand convex platens for forming, respectively, convex and concavesurfaces on the lens blank, the radius of curvature (r₁) of the concaveplaten and the radius of curvature (r₂) of the convex platen eachcorresponding substantially to the relationship

${r_{1} + r_{2}} = {t\left( \frac{n - 1}{n} \right)}$wherein t represents the thickness of the lens blank and n is the indexof refraction;

placing a volume of a polymerizable composition on the concave platen;and

heating and pressing the platens together with the lens blank betweenthem, the heating and pressing being such as to cause the lens blank todeform and to conform one surface to the convex platen and to cause thepolymerizable composition to polymerize and form a transparent layer ofnon-uniform thickness conforming to the concave platen, with the layerthus formed in situ having its maximum thickness in the central regionof the lens and diminishing gradually in thickness radially towards theperiphery of the lens.

The advantageous method of the invention allows the manufacture oflenses which have high impact strength and a high scratch-resistantconvex surface.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, as well as other objectsand further features thereof reference is made to the following detaileddescription of various preferred embodiments thereof taken inconjunction with the accompanying drawings wherein:

FIG. 1 is a partially schematic, side cross-sectional view of apreferred embodiment of a lens blank which can be used in themanufacture of a plastic lens according to the invention havingsubstantially no optical power;

FIG. 2 is a partially schematic, perspective view of one type of apress-forming apparatus suitable for carrying out the method of theinvention;

FIG. 3 is a partially schematic, side cross-sectional view of theapparatus illustrated in FIG. 2 showing the carrying out of one step ofthe method of the invention;

FIG. 4 is a partially schematic, side cross-sectional view of theapparatus illustrated in FIG. 2 showing the carrying out of a heatingand pressing step of the method of the invention;

FIG. 5 is a partially schematic, side cross-sectional view of theapparatus illustrated in FIG. 2 showing a lens-removing step accordingto the method of the invention; and

FIG. 6 is a partially schematic, side cross-sectional view of apreferred embodiment of a shaped plastic lens according to the inventionhaving substantially no optical power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described previously, the present invention is directed to shapedplastic lenses having substantially no optical power and to a method forthe production of such lenses. As applied to a plastic lens of theinvention, reference to a lens of substantially no optical power refers,in general, to the absence of magnification or demagnification. Thus, alens will be considered as having substantially no optical power wherethe power is sufficiently low as not to be discernible or detectable bythe human eye or where the power is within the limits of a publishedindustry standard for no power lenses. The production of such lensesaccording to the invention requires substantial adherence to therequirement of lens-forming platens having predetermined radii ofcurvature surfaces which result, under the heating and pressureconditions utilized according to the method of the invention, in theformation of shaped plastic lenses which are of non-uniform thickness,with the maximum thickness being in the central region of the lens andthe thickness diminishing gradually radially towards the periphery ofthe lens. Thus, the radii of curvature of the respective platens usedfor forming the concave and convex surfaces of the lenses of theinvention conform to an important relationship which is described ingreater detail hereinafter and which is predetermined to provide lensesof substantially no optical power.

The requirements for producing lenses of the invention havingsubstantially no optical power can be better understood by reference tothe mathematical formula (I) for the principal focus (F) of a thick lensof thickness (t) disclosed in the Handbook of Chemistry and Physics53^(rd) edition, 1972, published by the Chemical Rubber Company, pageF-85, as follows:

$\begin{matrix}{F = \frac{{nr}_{1}r_{2}}{\left( {n - 1} \right)\left\lbrack {{n\left( {r_{1} + r_{2}} \right)} - {t\left( {n - 1} \right)}} \right\rbrack}} & (I)\end{matrix}$where r₁ and r₂ represent the radii of curvature of the lens and n isthe index of refraction.

In the case of a lens of zero power, F is equal to infinity, in whichcase:n(r ₁ +r ₂)=(n−1)t  (II)Assuming an index of refraction (n) of 1.5, the radii of curvature, (r₁and r₂) relate to the thickness of the lens according to the formular ₁ +r ₂ =t/3Thus, where a composite laminate of a thickness of 0.100 inch (100 mils)is to be formed into a lens using a platen having a concave surface witha radius of curvature (r₁) of 3.514 inches (in order to form the convexside of the lens) it will be seen that the platen used to form theconcave side of the lens will have a convex surface having a radius ofcurvature (r₂) of 3.481 inches.

In contrast, and as is known in the art, the optical power (P) of a lensof uniform thickness (T) is represented by the formula

$\begin{matrix}{{P = {{- P_{\circ}^{2}}{T\left( {\frac{1}{n - 1} - \frac{1}{n}} \right)}}},} & ({IV})\end{matrix}$where T is expressed in meters. If the index of refraction (n) is 1.5and the nominal power (P), which is equal to the square root of theproduct of the powers of each of the opposed surfaces, is six, then

$\begin{matrix}{P = {{- 36}{T\left( {\frac{1}{1.5 - 1} - \frac{1}{1.5}} \right)}}} & (V)\end{matrix}$andP=−48T  (VI)It can be calculated from formula VI thatP=−0.00122t  (VII)where the thickness (t) is expressed in mils. The power (in diopters) oflenses of different thickness can be calculated readily, using formulaVII and examples of the power of lenses of different uniform thicknessare set forth in the following TABLE I wherein focal length is expressedin meters.

TABLE I t(mils) P (diopters) Focal Length 30 −0.0366 −27.3 45 −0.0549−18.2 60 −0.0732 −13.66 75 −0.0915 −10.93 90 −0.1098 −9.11 100 −0.1220−8.20

It will be seen from inspection of formula VII and from the data inTABLE I that an increase in the thickness of a lens of uniform thicknessresults in an increase in power. Thus, where lens thickness is increasedfor the realization of such desirable attributes as improved rigidityand durability, there is an accompanying and undesirable increase inlens power.

The requirements for the lens-forming surfaces of platens used for theproduction of lenses of the invention having substantially no power andnon-uniform thickness can be better understood by considering the radiiof curvature of platens useful for forming lenses of uniform thickness.For example, an “onion” lens having opposed convex and concave sides anduniform thickness can be analogized to concentric rings of an onionslice. Each onion ring of the same and uniform thickness is defined byconvex and concave radii. These radii have different values for eachslice. The respective radii for each slice also vary with progression ofthe rings outwardly to the onion surface. Transparent plastic substratematerials, by analogy to such rings, can be molded into lenses ofuniform thickness and the requirements of radii of curvature for platenscan be determined readily by analogy to the geometry of an onion. Suchlenses, however, have optical power which, as described previously,increases with thickness.

Plastic lenses having a convex surface of high scratch-resistantthermoplastic material can be produced according to the invention byusing platens of different predetermined radii of curvature andthermoplastic substrate materials and shaping conditions of heat andpressure, in conjunction with forming a layer of non-uniform thicknessby in situ polymerization, that negate the development of optical powerand that promote instead the formation of lenses of non-uniform overallthickness and substantially no optical power. The particularrequirements of radii of curvature and the requirements in respect ofthe materials and shaping conditions that permit the production oflenses of the invention are described in detail hereinafter.

As described previously, the method of the invention relates generallyto the formation of shaped plastic lenses of non-uniform thicknesshaving substantially no optical power wherein a layer of non-uniformthickness is formed via in situ polymerization. Thus, generally, a lensblank used to form lenses according to the invention can be a planarstructure comprising a substantially uniformly thick layer or layers ofsuitable thermoplastic material(s). The method of the invention will bedescribed further in detail with respect to the preferred embodiment ofthe invention wherein the lens blank used to form lenses according tothe invention is a composite structure comprising a layer of alight-polarizing material between layers of thermoplastic substratematerial.

Referring now to FIG. 1, there is shown, a laminated structure 10 oflayers, or sheets, 12, 14, 16 and 18 from which a plasticlight-polarizing lens according to the invention can be formed. Layer,or sheet, 12 comprises a molecularly oriented light-polarizing materialwhich provides the light-polarizing functionality of the preferredshaped lens of the invention. Typically, light-polarizing layer 12comprises a linear molecularly oriented dichroic material having athickness in the range of from about 0.1 to about 3 mils (about 0.0025to about 0.076 mm) and preferably about 0.5 mils (about 0.0125 mm).

A preferred material for use as light-polarizing layer 12 is a layer ofstretched, or oriented, poly(vinyl alcohol) of about five mil thicknessstained according to known methods with a dichroic dye such as iodine.Such a polarizing material will also preferably be borated for improvedstability. Suitable polarizing layers of this type can be preparedutilizing methods described in Reissue U.S. Pat. No. Re. 23,297 and inU.S. Pat. No. 4,166,871. Another preferred polarizing material is astretched poly(vinyl alcohol) sheet containing polyvinylenelight-polarizing species such as may be provided by hydrochloric acidvapor processing according to known methods. Preferably, such polarizingmaterial will be borated for improved stability. Suitablelight-polarizing materials of this type can be prepared by the methoddescribed in U.S. Pat. No. 2,445,555. Other light-polarizing materialscan, however, be employed and methods for their production can be foundin U.S. Pat. Nos. 2,237,567, 2,527,400 and 2,554,850.

In the production of light polarizers, one or more support, or carrier,sheets can be employed to improve the durability and handlingcharacteristics of the light-polarizing material. Support sheets ofcellulose acetate, cellulose triacetate, cellulose acetate butyrate(CAB), or of other polymeric material can be used for this purpose. Anadhesive can be used to promote desired bonding without forming bubbles,haze or other visible defects. Suitable adhesives are known in the art.

Layers 14 and 16 comprise thermoplastic material, which can be molded orshaped to the desired curvature for lenses of the invention. Transparentthermoplastic resins known to be useful in the production of opticalelements can be used for layers 14 and 16. Typical suitablethermoplastic materials include poly (methyl methacrylate), polystyrene,polycarbonate and cellulosic thermoplastic materials such as cellulosenitrate, cellulose acetate, cellulose triacetate, cellulose acetatepropionate, cellulose acetate butyrate and ethyl cellulose. Generally,suitable materials are those which are transparent and which exhibitgood durability and moldability. In addition, it will be beneficial thatthe resinous materials of layers 14 and 16 exhibit low birefringence andthat they exhibit good heat resistance and moisture resistance. Layers14 and 16 of resinous material can be selected from the resinousmaterials previously mentioned, although other materials can be used. Itwill be apparent that the moldability or processability of the resinousmaterials comprising layers 14 and 16 has to be taken into considerationinsofar as the required molding or lens-shaping conditions oftemperature and pressure may influence the physical and opticalproperties of the light polarizer confined between such layers. Thus,layers 14 and 16 comprise a thermoplastic material moldable into acurved lens according to the invention without degradation or otherharmful and undesirable influence on light polarizer layer 12.

In general, poly (methyl methacrylate) resins exhibit good durability,transparency and processability and the beneficial attributes andlimitations of poly (methyl methacrylate) and others of theaforementioned materials, insofar as their adaptability to theproduction of optical elements is concerned, are known and described,for example, in U.S. Pat. Nos. 4,986,641 and 5,043,405. Homopolymers ofmethyl methacrylate and other methacrylate polymers such as norbornylmethacrylate can be used, as can methacrylic copolymers which includerepeating units from methyl methacrylate and from other copolymerizablemonomers. Examples of such homopolymers and copolymers can be found inthe aforementioned U.S. Pat. Nos. 4,985,648 and 5,043,405.

Preferred materials for layers 14 and 16 are cellulose acetate butyrateand polycarbonate. Cellulose acetate butyrate is preferred for use inlayer 14 because it has a low coefficient of stress. Polycarbonate is apreferred material for layer 16 because of its high impact-resistantproperties. In a particularly preferred embodiment layer 14 comprises anapproximately 0.005 inch (0.127 mm) thick layer of cellulose acetatebuytrate and layer 16 comprises an approximately 0.015 to 0.030 inch(0.381 to 0.762 mm) thick layer of colored polycarbonate. The colorationmay be provided by incorporating visible dyes in layer 16 to providecontrast and aesthetic qualities. Optionally, and preferably, the lensblank includes an approximately 0.015 to 0.030 inch (0.381 to 0,762 mm)thick clear polycarbonate layer 18. In this preferred embodiment theconcave surface of the lens preferably includes a hardcoat, or a highscratch resistant layer, since polycarbonate typically scratches easily.It is preferred to utilize a clear polycarbonate layer with a hardcoatlayer as layer 18.

Layers 14, 16 and 18 can each comprise one or more layers. Good resultscan be obtained using a single layer for each of respective layers 14,16 and 18. Generally, it is preferred that layer 16 and optional layer18, when present, have a thickness greater than that of layer 14. Adifferential in thickness permits light polarizing material 12 to bepositioned in lens 50 (FIG. 6) more closely to the convex surface of thelens than to the concave surface. It is advantageous to have the layerof light-polarizing material 12 located as close as possible to theconvex surface of the lens so that there is the least opportunity forthe material through which light must pass before the light strikes thelight-polarizing material to interfere with the absorption of polarizedlight. Said another way, the material though which light passes beforestriking the light-polarizing material should not have any substantialbirefringence. In addition, the employment of one or more layers of athickness substantially greater than that of the other layer provides agreater latitude of processing, for example, temperature and pressure,conditions which can be employed in the lens-shaping operation withoutdetrimental influence on the physical integrity and optical propertiesof light-polarizer 12. Optional layer 18 may be the same thickness aslayer 16 or may be of different thickness.

In a particularly preferred shaped lens of the invention, layer 14comprises an approximately 0.005 inch (0.127 mm) thick layer ofcellulose acetate butyrate, layer 16 comprises an approximately 0.015inch (0.381 mm) thick layer of colored polycarbonate and layer 18 anapproximately 0.030 inch (0.762) thick layer of clear polycarbonatehaving a hardcoat layer, i.e., a layer of a high scratch-resistantmaterial, on the outer surface.

As described previously, the layers of the lens bank may be adhered toeach other by adhesives. Various adhesives can be employed for thispurpose, provided that they are substantially transparent and provide ahaze-free lamination free of bubbles and other unacceptable and visibledefects. The respective layers 14, 16 and, when present, 18 can, ifdesired, include various additives for their known and predeterminedeffects. Stabilizers such as ultraviolet light absorbers, antioxidants,mold-release agents, lubricating agents, surface active agents andelastomers can be present. Dyes such as gray, yellow, blue or othercolored dyes can also be employed to obtain a lens of a desired densityor color. Layer 16, or layer 18, when present, can include anabrasion-resistant layer, or coating, to improve the resistance of theconcave surface of the lenses to scratching and abrasion. Such a layercan comprise, for example, a thermosetting, cross-linked polymericmaterial.

The laminate composite structure 10 shown in FIG. 1 and from which alight-polarizing lens structure 50 such as is shown in FIG. 6 can beproduced, can be produced and used in various manners. For example,unitary blanks having the structure shown in FIG. 1 can be formed andthen molded, or shaped, to a desired lens, each blank being produced bya lamination of precut components 12, 14, 16 and 18 of square, round,elliptical or other shapes. Such blanks can be formed under heat andpressure into a lens according to the invention and the edges thereofcan be ground in known manner suitable to adapt them to placement intospectacle frames. Preferably, a composite structure of finite or endlesslength can be formed by a continuous or semi-continuous method wherebywebs or pieces of thermoplastic sheet material are adhered to theopposing sides of a light-polarizing layer. Individual blanks can thenbe cut from the laminate structure using a cutting apparatus such as asaw, knife, laser, etc. Such a cutting operation can be carried out atany time prior to the shaping thereof in an apparatus such as apress-forming apparatus.

Individual blanks can be pretreated as desired before shaping. Forexample, lens blanks of predetermined dimensions suited for theparticular forming apparatus employed can be heated and placedimmediately or after substantial cooling into the forming apparatus.

The method of the invention by which lenses having substantially nooptical power are formed will now be described in connection with FIG's.2 through 5.

The forming process can be by apparatus of the type shown in FIG. 2. Theapparatus includes concave platen 24, convex platen 26, means fordriving the platens into and out of pressure-applying relationship witheach other and means for alternately heating and cooling the platensduring each pressure-applying interval.

Concave platen 24 includes glass member 28 having smooth concave formingsurface 30, shaft 32 operatively connected to a suitable drive means,fluid chamber 33, fluid inlet coupling 34 and fluid outlet coupling 36.

Convex platen 26 includes glass member 38 having convex forming surface40, fixed support means 42, fluid chamber 43, fluid inlet coupling 44and fluid outlet coupling 46.

As discussed previously, the respective concave and convex formingsurfaces 30 and 40 have different radii of curvature which correspondsubstantially to the relationship expressed by formula II.

The drive means includes a suitable hydraulic piston and cylinderarrangement 47 operatively connected to platen 24 for moving platen 24into and out of pressure-applying relationship with platen 26.

The heating and cooling means for both the platens includes three wayvalve means 49, heating fluid conduit 51, cooling fluid conduit 53 andfluid inlet 55 connecting one of the three way valves to each of fluidinlet couplings 34 and 44 of platens 24 and 26 respectively.

Referring now to FIG. 3, laminated lens blank structure 22 is placed inconcave platen 24 so that relatively thin sheet 14 faces concave platen24 thereby locating light polarizing layer 12 relatively near theconcave platen. Also placed on the smooth concave forming surface 30 ofplaten 24 is a volume of a polymerizable composition 57 comprising amonomer or an oligomer and a polymerization iniatiator. Generally, thevolume of polymerizable composition 57 is determined by the requirementto obtain sufficient coverage on the surface of lens blank 22 and is afunction of the lens curvature and size. Typically, a volume of fromabout 0.1 to about 0.8 ml of the polymerizable composition issufficient. As has been discussed previously, under the conditions ofheat and pressure applied by the molding apparatus, polymerizablecomposition 57 forms a layer of non-uniform thickness on the convexsurface of the lens so as to provide a lens having substantially nooptical power.

Any suitable monomer or oligomer which will provide an optically clear,durable, scratch resistant, high impact-resistant polymeric film ofnon-uniform thickness in accordance with the method of the invention maybe used. Typical suitable monomeric or oligomeric materials include, forexample, acrylates, methacrylates, urethanes, amines and inorganicmaterials such as, for example, polysiloxanes. The polymerizablecomposition may include a single monomer or oligomer or a mixturethereof. Any suitable polymerization initiator material may be used. Thepolymerizable composition may also include other additives to providetheir known and predetermined effects. It is preferred to includeelastomers such as, for example, nitrocellulose or cellulose acetatebutyrate to inhibit cracking of the layer of non-uniform thicknessformed from the polymerizable composition. A particularly preferredpolymerizable composition for use in accordance with the inventioncomprises a mixture of tetraethylene glycol methacrylate anddipentaerythritol pentacrylate monomers. The polymerizable compositionpreferably includes an inhibitor such as hydroquinone.

The polymerization of the monomeric or oligomeric material may becarried out by any suitable polymerization technique such as freeradical polymerization, cationic polymerization, ultravioletpolymerization and thermal cure polymerization. It is preferred toemploy free radical polymerization.

In accordance with the method of the invention, the concave and convexplatens are then brought into pressure-applying relationship as shown inFIG. 4 to form, or shape, the laminated lens blank structure 22, underthe combined effects of heat and pressure, into a shaped structure andto form a layer of non-uniform thickness from the polymerizablecomposition thereby forming a shaped lens 50 (FIG. 6) havingsubstantially no optical power. The layer of non-uniform thickness, ischaracterized by having maximum thickness in the central region of thelayer thus providing a lens 50 also having maximum thickness in thecentral region of the lens.

The amount of pressure applied in any particular instance will vary withthe particular nature of the lens blank structure, such as lens blank22, especially the nature of the thermoplastic materials in the lensblank structure and with the temperatures of the forming surfaces 30 and40. In the case of a composite structure comprising a light polarizer ofthe preferred type described above laminated between sheets of celluloseacetate butyrate and polycarbonate, pressures in the range of from about250 to about 800 lbs/in² (1724 to 5516 kilopascals) of lens area can besuitably employed. A preferred pressure is about 425 lbs/in² (2930 kPa).

While pressure is applied to the laminated structure 22, as described,the platens are heated by passing hot water through chambers 33 and 43of platens 24 and 26, respectively. Surfaces 30 and 40 are continuallyheated sufficiently to cause deformation of the polarizer layer 12 andthe thermoplastic layers 14 and 16, and layer 18 when present, andconformation of the surface of layer 16, or layer 18, when present, tothe forming surface 40 of platen 26 as well as conformation of thesurface of layer 14 to the layer of non-uniform thickness of thehigh-impact resistant polymeric material formed in situ according to theinvention and conformation of the outer surface of the layer ofnon-uniform thickness to the forming surface 30 of platen 24. Thus, theapplication of heat and pressure is sufficient to cause the deformationof the lens blank 22 such that one surface of the blank conforms to theforming surface 40 of platen 26 and the outer surface of the layer ofnon-uniform thickness of high-impact resistant polymeric material formedin situ according to the invention conforms to the forming surface 30 ofplaten 24 as well as causing the other surface of the lens blank toconform to the inner surface of the layer of non-uniform thickness.

The employment of conditions sufficient to cause deformation of the lensblank and polymerization of the polymerizable composition with theaccompanying formation of a layer of non-uniform thickness ofhigh-impact-resistant material assures that the lens produced accordingto the invention has an overall non-uniform thickness.

The method of the invention can be employed for the production of lenseswhich are relatively thick and which desirably have, therefore, thedurability associated with such thickness. Lenses of widely varyingthicknesses can be produced according to the invention. The method isparticularly suitable for the production of relatively thick lenseswhich, if of uniform thickness, would exhibit unacceptable opticalpower. The method is particularly useful for the production ofsubstantially no optical power lenses of a thickness of about 50 mils(1.27 mm) or greater, for example, in the range of from about 50 to 150mils (1.27 to 3.81 mm).

In the production of lenses according to the invention it is convenientto utilize a platen 24 having a forming surface 30 which corresponds tothe predetermined curvature of the convex side of the lens to be formed.It is apparent that the convex surface of the layer 51 (FIG. 6) which isformed against forming surface 30 serves as the outer surface of thelens 50 (FIG. 6). One suitable radius of curvature for forming surface30 for forming a convex lens surface is 3.514 inches.

Using formula III, appropriate for calculating the radii of curvaturerequired for lenses having substantially no optical power, and assumingthat the radius of curvature of forming surface 30 (r₁) is 3.514 inches,the radius of curvature of the opposed lens surface (and platen) can bedetermined for the production of a lens of any nominal thickness.

TABLE II shows, for various lenses which can be produced according tothe method of the invention, the radii of curvature for the convex andconcave forming surfaces, the center thickness, the edge thickness, thediopter and the optical power.

TABLE II Convex Concave Center Edge Optical Radii Radii ThicknessThickness* Power (inch) (inch) (inch) (inch) Diopter (diopter) 3.5143.494 0.060 0.057 6 −0.001 3.514 3.486 0.075 0.071 6 −0.001 2.633 2.6130.060 0.053 8 −0.001 2.633 2.605 0.075 0.067 8 −0.001 *Edge is 1.5” fromthe center of the lens.

The conditions of temperature and pressure sufficient to causedeformation of the lens blank and to cause polymerization of thepolymerizable composition during production of lenses according to theinvention cause the finished lenses to conform to the radii of curvatureof the forming surfaces of the platens. The requisite temperature forcreating deformation of the lens blank and polymerization of thepolymerizable composition to form the layer of non-uniform thicknesswill vary with the chemical composition of the poymeric materials. Usingcellulose acetate butyrate and polycarbonate sheets, moldingtemperatures of from about 150° F. to about 200° F. A preferred moldingtemperature is heating at 170° F. for 70 seconds.

The temperatures of the forming surfaces of the platens can becontrolled by the passage of heated water and cooled water, as describedpreviously. The platens are preferably preheated i.e., prior toplacement of the lens blank therebetween, and are heated to therequisite forming temperature for a heating cycle sufficient to form thedesired shaped lens. For example, the forming surfaces of the platenscan be preheated for about 20 seconds to about 170° F. in the case ofcellulose acetate butyrate and polycarbonate materials prior to placingthe lens blank into the mold and closing the mold for about 70 secondsduring heating. The mold surfaces are then heated to the requisiteforming temperature by the passage of heated water through the platensand the temperature is maintained for a duration, e.g., about 70seconds, sufficient for the desired lens formation. Thereafter, thetemperature of forming surfaces 30 and 40 is reduced by passage of acooling fluid such as relatively cool water through chambers 33 and 43of the platens. The cooling fluid is passed through the platens for aperiod, for example, of about 50 seconds before the press is opened.

Hot water is supplied to the platens through conduit 51 and therelatively cool water is supplied through conduit 53. During the heatingcycle, valve 49 opens a connecting passage between conduit 51 and inlet55 and closes conduit 53. Oppositely, during the cooling cycle, thevalve 49 opens a connecting passage between conduit 53 and inlet 55 andcloses conduit 51. The transition from the heating cycle to the coolingcycle is carried out by operating valve 49 to mix cool water with thehot water until the hot water is completely displaced by cool water.Transition from the cooling cycle to the heating cycle is carried out byreversing the operation.

After the cooling operation, platens 24 and 26 are separated to relievethe pressure on the shaped lens and permit its removal, as shown in FIG.5. The shaped lens may adhere to one of the forming surfaces in whichcase it may be removed by a stream of compressed air supplied by airnozzle 48.

FIG. 6 illustrates a shaped light-polarizing lens 50, concave on theside formed by concave platen 26 and convex on the side formed by platen24. There is seen layer 60 of non-uniform thickness which has highscratch resistance and which forms the convex surface of lens 50.

Using the apparatus shown in FIG. 2, and employing the conditions ofpressure and temperature described above herein, shaped lenses ofsubstantially no optical power which have a convex surface of a highscratch-resistant and high impact-resistant material can beadvantageously provided. It will be appreciated, however, that otherapparatus can be used and variations in process conditions, such asheating and cooling cycles, may be employed, depending upon theparticular materials present in the lens blank and the polymerizablecomposition.

Although the invention has been described in detail with respect tovarious preferred embodiments thereof, the invention is not limitedthereto, but rather those skilled in the art will recognize thatvariations and modifications may be made therein which are within thespirit of the invention and the scope of the appended claims.

1. A shaped plastic lens convex on one side and concave on the otherside and having substantially no optical power comprising a firstsubstantially uniformly thick layer of thermoplastic polymeric material,a second substantially uniformly thick layer of thermoplastic polymericmaterial and a third thermoplastic layer of non-uniform thickness andhaving high scratch resistance, said third layer having maximumthickness in the central region thereof and diminishing gradually inthickness radially toward the periphery thereof, wherein said secondsubstantially uniformly thick layer forms said concave side of the lensand said third layer forms said convex side of the lens.
 2. The shapedplastic lens as defined in claim 1 and further including a layer of alight-polarizing material positioned in said first layer of said lens.3. The shaped plastic lens as defined in claim 2 wherein said firstlayer of thermoplastic material comprises cellulose triacetate orcellulose acetate butyrate and said second layer of thermoplasticmaterial comprises polycarbonate, said light-polarizing layer beingpositioned between said cellulose triacetate or cellulose acetatebutyrate layer and said polycarbonate layer and said polycarbonate layerforming said concave side of said lens.
 4. The shaped plastic lens asdefined in claim 3 wherein said polycarbonate layer of said lenscomprises a colored layer of polycarbonate and a clear layer ofpolycarbonate having an outer surface of a high scratch-resistantmaterial, said high scratch-resistant material forming said concavesurface of said lens.
 5. The shaped plastic lens as defined in claim 4wherein said lightpolarizing layer is positioned closer to said convexside of said lens than to said concave side of said lens.
 6. The shapedplastic lens as defined in claim 1 wherein said third layer comprises apolymer of a tetraethylene glycol methacrylate monomer and adipentaerythritol pentacrylate monomer.
 7. The shaped plastic lens asdefined in claim 2 wherein said third layer comprises a polymer of atetraethylene glycol methacrylate monomer and a dipentaerythritolpentacrylate monomer.
 8. The shaped plastic lens as defined in claim 7wherein said lightpolarizing layer is positioned closer to said convexside of said lens than to said concave side of said lens.
 9. The shapedplastic lens as defined in claim 8 wherein said first layer ofthermoplastic material comprises cellulose triacetate or celluloseacetate butyrate and said second layer of thermoplastic materialcomprises polycarbonate, said lightpolarizing layer being positionedbetween said cellulose triacetate or cellulose acetate butyrate layerand said polycarbonate layer.